I don't have hard data either. But ask any old Mac developer on Twitter whether they're doing better now than ten years ago, and I bet a majority would disagree.
For one thing, the rise of mobile app stores has destroyed the perceived value of software. A $50 app now seems very expensive to most, whereas it was mid-priced back in 2008. Yet the Mac App Store has failed to bring in the mass audience that would compensate for the lower unit prices.